Two polysaccharides, cellulose and hemicellulose, make up approximately 70% to 85% of lignocellulose, one which in turn makes up the vast majority of woody biomass and agricultural residues.
One particular derivative obtainable from these polysaccharides is xylitol, a five-carbon sugar alcohol, which has several applications and potential use in some industries that may include food, odontological and pharmaceutical.
Industrially, xylitol may be produced from the reduction of pure xylose via acid hydrolysis of xylan containing products such as hardwoods or corn cobs. Such a process contains multiple steps, which may include production of xylose by an initial acid decomposition of xylan containing natural products; concentrating the hydrolysis solution to remove impurities; catalytic hydrogenation of xylose to xylitol under high pressure hydrogen gas (up to 50 atm) at elevated temperatures (commonly above 160° C.); and then purification and isolation of the xylitol. This multi-step process is laborious, costly, energy intensive and environmental unfriendly. Moreover, the yield of xylitol attained is only 50% to 60% of the xylan present in the raw materials. In addition, due to the use of the high pressure hydrogen gas, sophisticated hydrogenation facilities are required which safety is a major concern.
Xylitol may also be synthesized by other similar multi-step processes with modifications made to some of the steps within, such as using basic hydrolysis or enzymatic hydrolysis instead of acidic components etc.
Other modifications may include the use of xylitol producing microbial strains in the fermentation of xylose from crude hydrolysate to xylitol. However, such bioconversion suffers from lackluster yields due to the presence of microbial growth inhibitors that are generated from upstream degradation of cellulose or hemicellulose via chemical (acid or base) hydrolysis. Microbial toxicity is also associated with fermentation variables such as microbial physiological growth conditions, dissolved oxygen concentration and pH of the medium. In general, biomass hydrolysate inhibitors comprising sugar or lignin degradation products, derived from lignocellulosic structure, and heavy metal ions remain a serious drawback for using bio-processes.
Accordingly, there is a need for a more effective production process of a sugar alcohol such as xylitol that ameliorates the above limitations.
There is a need for the reduction of steps in the above process that overcomes, or at least ameliorates, one or more of the disadvantages described above.